The present invention relates to a transmission device using a flexible gear (hereafter referred to as a flexible type transmission device, when applicable) which provides a speed-reduced output using a large number of external teeth on a flexible member capable of flexing substantially in an elliptical manner and a large number of internal teeth capable of meshing partially with the external teeth. The flexible type transmission device can be used not only as a speed-reducing device, but also as a speed-increasing device and a differential device.
A flexible type transmission device generally comprises: a fixed case (serving as a circular spline) including a large number of internal teeth formed on the inner periphery thereof; a flexible member (serving as a flexible spline) inserted into the fixed case and including a large number of external teeth formed on the outer periphery thereof with the number of the external teeth slightly smaller than the number of the internal teeth of the fixed case, the external teeth being capable of partially meshing with the internal teeth of the fixed case when the flexible member is flexed substantially in an elliptical manner; a wave generator accommodated within the flexible member and rotatable with respect to the flexible member for applying a substantially elliptical flexural deflection to the flexible member; and, an output member connected to the flexible member. To rotatably support the output member on the fixed case, interposed between the fixed case and output member is a cross roller bearing composed of a large number of cylindrical-shaped rollers arranged in the peripheral direction thereof with the inclining directions thereof alternately reversed. Alternatively, there is interposed a taper roller bearing composed of two roller races, each roller race including a large number of cylindrical-shaped rollers disposed in the peripheral direction and spaced from one another, the rollers of the respective roller races being inclined in the opposite directions with respect to the axial direction.
However, the above-noted support structure for the flexible type transmission device suffers from a problem in that since the outer surfaces of the rollers of the cross roller bearing or taper roller bearing are slidingly contacted with the output member and the race surfaces of the fixed case during the rotation of the output shaft, the rollers, output member and fixed case are worn out early and thus the service lift of them is shortened. Further, the cross roller bearing and taper roller bearing are both expensive generally.